In X-ray radiography an x-ray image of an elongate body such as the entire spine or the legs of a patient, may have to be obtained. Long length images are mostly taken to perform length and angle measurements on a radiation image of a subject.
In Computed Radiography (CR), such a long length image is generated by subjecting a number of Imaging Plates (IP), such as photo-stimulable phosphor plates, which are organized in a partially overlapping disposition, to an x-ray image of the elongate body. Each of the imaging plates carries an image of a part of the elongate body. After exposure, the individual imaging plates are read out so as to obtain partial images of the elongate body and finally a long length image is created by stitching these partial images. Accurate alignment and measurement can be obtained by superimposing an object of known geometry of radiation attenuating material such as a grid covering the region to be imaged and correcting and aligning the partial images to reconstruct the geometry of said grid. Such methods are described in European patent applications EP0919856 and EP0866342.
In recent years, Digital Radiography (DR) has become a valuable alternative for CR. The flat panel detectors (FPD) used in DR are more costly than the IP's for CR, so an alternative to the one-shot long length imaging technique of CR is needed. This is achieved by taking plural partial images of an elongate body by moving the position of the FPD while tilting the X-ray tube or moving the X-ray tube parallel to the FPD. During this movement, the patient may move, hereby introducing artifacts which need to be compensated in the full image re-composition from the partial images. The applied compensations for the correction of the patient movement may lead to inaccurate measurements. Inaccurate FPD positioning also decreases the accuracy of measurements done in the composite image.
An article by Xiaohui Wang, “Fully automatic and reference-marker-free image stitching method for full-spine and full-leg imaging with computed radiography”, Proceedings of SPIE, vol. 5368, 1 Jan. 2004, pages 361-369 discloses image stitching of partial images.
In the article by Simon T. Y. Suen et al, “Photographic stitching with optimized object and color matching based on image derivatives”, Optics Express, Vol. 15, No. 12, 1 Jun. 2007, different stitching methods are compared. The article discloses a theoretical comparison.
It is an object of the present invention to overcome the drawbacks of the prior art.